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PostPosted: Tue Sep 24, 2019 11:40 am 
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I put together a Tramp head. When I switched it on to test voltage with no tubes the LED lit up for a couple seconds then died. Fuse blown. I took voltage readings of the caps after this and they all report zero.

One oddity is that I broke the 6l6/6v6 toggle by over tightening the bolt - the whole thing just fell apart. I wired it direct to 6v6, or so I think. Other than that everything is by the book.

Does anyone have any clues on where to start to debug this?


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PostPosted: Tue Sep 24, 2019 4:03 pm 
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More pics at different angles on the power xfmr end, Difficult to see where your wires begin and end. Also, I have read of fuse holder being shorted w/ excessive heat on terminals. Might want to UNPLUG and do continuity checks. Note also that that selector switch seems to be wired in an different manner than I've seen before, usually terminals 1,2, and 3. That's all I can suggest for now.

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PostPosted: Tue Sep 24, 2019 6:08 pm 
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Had a thought on narrowing it down. Disconnect and insulate red leads from board and insulate them. Install new fuse and power up, if fuse blows, then it's definitely the power wiring and concentrate there. Need to get properly rated spare fuses, too, just in case ;) Added some pics, may help, may not :hmmm:


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PostPosted: Tue Sep 24, 2019 8:15 pm 
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Thanks for giving me some things to check.

The output ohm selector is wired to the diagram - it's just in there upside down. yellow to 1 , green to 2, orange to 3 and A to output jack tip.

I'll check the fuse holder first thing, once I pick up some fuses. One thing - on the amp it says 120v 2a / 240v 1a. Does this mean my 120 volt should have a 2 amp fuse? It came with a 1 amp 250 volt fuse.

I've been thinking about it and I'm guessing it's a mechanical short under the eyelet board - stray wire clip or solder or something, but I think it's a good idea to ask here for clues before I start desoldering to look under there.

Here's a few more pictures. (excuse my crap camera)

Some of the early solders look dull. I was using lead free solder at first, but I didn't like working with it and switched to the good old poison stuff.


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PostPosted: Tue Sep 24, 2019 9:59 pm 
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Like Hank said, disconnect the red wires from the power transformer to the board, insulate them and test again. Also carefully check the AC high voltage from each red wire to ground. Check the heater connections on the tube sockets, too.

The fuse should be 2 amp for 120-volt operation.

Good to check for shorts, too. And you can look up "dim bulb tester" on the internet and try that. It's always good to use one the first time you power up an amp.


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PostPosted: Tue Sep 24, 2019 10:08 pm 
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Check your unused xfmr wires. Did you clip and insulate each of the the unused wires with heat shrink?

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PostPosted: Wed Sep 25, 2019 2:45 pm 
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I clipped the unused transformer leads and then heat shrunk them together, no leads poking out to touch, but not individual. The kit was a little light on tubing. I have some on the way and I'll redo them at that time - just in case.

I made a current limiter like Uncle Doug's here https://www.youtube.com/watch?v=wRFRwOnLsZI I have to get a bulb for it.

I got new fuses which are 2A 250V slow-blow. I think that's right. Correct me if I'm wrong.

I also picked up a crazy cold and I'm going to take a break from this until I'm feeling better. I'll post the results of my debugging when I get back on it.


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PostPosted: Wed Sep 25, 2019 3:12 pm 
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To quote on of your previous posts: "I'll check the fuse holder first thing, once I pick up some fuses. One thing - on the amp it says 120v 2a / 240v 1a." That is correct. Don't use the 250V 2A fuse, you could possibly fry the amp :!: Look for a slow-blow ( fast- blow won't work due to in-rush current @ start up) fuse with the rating listed on the back of the amp! Check the end of the fuse that blew (probably need a magnifying glass) :bugeye: , it should have the rating on it. Get the same kind.

Post when you get better.

Hope you get better soon. PS If you live anywhere allergies are bad, that might be the problem. I live Oklahoma and I'm taking them regularly at this time of year. :thumbsup:

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PostPosted: Wed Sep 25, 2019 9:37 pm 
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The Tramp should use a 1A Slow Blow fuse for 120 volt mains operation (USA, Canada).
Mine is a 240 Volt mains build (Australia) and I have always run a 500ma Slow Blow fuse (0.5A) since 2012.

Sounds to me like an error in the more recent documentation/labeling.


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PostPosted: Wed Sep 25, 2019 10:00 pm 
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Thanks. This is what is printed on the chassis. 120V 2A / 240V 1A. The bill of materials lists "FUSE SLO_BLO 1 AMP" and it came with a 1A fuse. I think the transformers have been changed since you built yours - so who knows.

Also, thanks for your past build thread full of quality pictures!


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PostPosted: Wed Sep 25, 2019 10:48 pm 
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Here's what I got in mine. https://www.mouser.com/Circuit-Protecti ... 13&FS=True 5 choices , all the same size. MXP or HXP suffix, looks like either one will do. EDIT: LittleFuse 313, rated 250V 1A came with the latest kit purchased 7-25-2019

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Last edited by Hankules on Thu Sep 26, 2019 1:49 pm, edited 1 time in total.

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PostPosted: Wed Sep 25, 2019 11:57 pm 
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Les537 wrote:
Thanks. This is what is printed on the chassis. 120V 2A / 240V 1A.


I would not trust the 2A fuse advice printed on the chassis until confirmed with Stephen, I suspect that might actually be an error.


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PostPosted: Thu Sep 26, 2019 1:26 am 
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Nice current limiter. There isn't much to them but they can save fuses and spark shows when powering up old equipment or new construction that has never had power before.

The schematic says the fuse is 1 amp for 120-volt operation. That would be 500mA for 240 volts like Snowy said. Most Trinity amps use a 2 amp fuse so maybe the lettering on the chassis was just carried over from the others and it's not quite right.

Anyway, the voltage rating on all these fuses is usually 250 volts, even if they are used at 120. It's the amperage that matters.

When you are feeling better, try the amp again with your current limiter and a 1 amp fuse. First with the transformer's red wires disconnected and no tubes installed. Once that works, connect the red wires and test again. With no tubes installed the voltages will be higher than the nominal values. Then put in the tubes and check the voltages again.


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PostPosted: Thu Sep 26, 2019 9:33 pm 
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Mine came with LittleFuse brand, type 313, rated 250V 1A came with the latest kit purchased 7-25-2019

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PostPosted: Sat Sep 28, 2019 5:59 pm 
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I'm back on my feet.

I got some 1 amp fuses and a 300 watt bulb for the current limiter.

I tested the fuse holder and it's not shorting. I looked under the eyelet board for shorts and there was nothing obvious, though I redid a couple solders that looked a little too close to each other.

I said some chants to various gods (hendrix, john lee hooker) and fired it up with no tubes. The LED lit up and the current limiter did not. It looked good. I measured DCV at the first 50uf cap with power level knob at idle and it read about 8 volts (instructions say to expect +400). The second cap read 430 volts. Instructions say to check at the rectifier pins which I do not understand as there is no rectifier tube. I shut it down.

I'm not sure what to do next. If I had to guess I would suspect the power pot, but I'm hoping someone with more experience might supply the next clue.

Thanks for any help!


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PostPosted: Sat Sep 28, 2019 11:09 pm 
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1)The two red wires from power xfmr that connect to the two diodes on the board (AC voltage) should read 630 VAC or over. The diodes are what convert AC current to DC. Be careful you have to use both Multi Meter probes for this 2)You use the power control to adjust the voltage at 1st 50 uF cap to 400 VDC in order to check the other voltage (clip black lead to chassis for ground and use red probe on cap eyelet). The usual advice is to put one hand in your back pocket and sit on it while using the other hand on the MM probe while checking voltages (no joke) :!: That's so if you get shocked it won't travel across your chest from one arm to the other (a heart stopping experience). Good luck and be safe. :thumbsup:

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PostPosted: Sun Sep 29, 2019 12:02 am 
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If you get 430 volts DC at the second 50uF capacitor (C13), that's a good sign.

The voltage at the first 50uF capacitor (C12) should vary with the power level control. When the control is full up it should read about the same as the voltage at C13. As Hank said, set the power level control so you get 400 volts at C12 once you get the tubes installed for the rest of the voltage testing.

"Rectifier" is the term for any circuit that converts AC to DC. It doesn't matter whether solid-state diodes or a vacuum tube do the work, it's still a rectifier. If it's a tube circuit, usually a single tube does the conversion, so the tube is just called a rectifier rather than a dual diode.


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PostPosted: Sun Sep 29, 2019 8:45 am 
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I want to thank you guys for all the help.

I tested the VRM (power level pot) with a 9v battery as explained in the trouble shooting instructions. It looks ok.

Next I bypassed the mosfet completely also explained in the trouble shooting instructions. It still read about 5-6 volts on the first cap, but at least it removed some possibilities.

I checked the diodes and resistors values that come before the first cap and everything looks ok.

When I'm less full of despair I will trace every lead to schematic to make sure they go to the right places and recheck every value (I did check them all at install). Failing that - something is going in the lake; me or the amp!


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PostPosted: Sun Sep 29, 2019 2:25 pm 
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Yes, recheck the wiring, resistors, and connections in the power supply area. Check the jumpers on the bottom of the board, too. Try checking the voltages at each connection in the power supply circuit and see where it stops. The sequence would be the diode cathodes, C13 (you say this is good), both ends of R23, MOSFET drain, MOSFET source, both ends of R20, C12.

Once that's working you can continue following the B+ chain and check the voltages at R17, C7, R10, C6, R9, R4.

You say the MOSFET is bypassed right now which is good. It's best to get an amp working properly before installing a VRM.


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PostPosted: Sun Sep 29, 2019 3:23 pm 
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I think I found it.

r23 XICON 100ohm 5 watt resistor is not letting anything through. I pulled it out of the circuit to be sure and it still measure infinite resistance.

That resistor leads to the first cap, C13. where I should be seeing 400+ VDC and only see 5 or 6.

This feels good. Does it sound logical?


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